io/system,widget/material: add decorations

Add the Decorations material widget and the related system
elements in preparation for the automatic window decoration
patch.

Signed-off-by: Pierre Curto <pierre.curto@gmail.com>

io/system/decoration.go

@@ -0,0 +1,112 @@
+package system
+
+import (
+	"strings"
+
+	"gioui.org/io/pointer"
+)
+
+// Action is a set of window decoration actions.
+type Action uint
+
+const (
+	// ActionMinimize minimizes a window.
+	ActionMinimize Action = 1 << iota
+	// ActionMaximize maximizes a window.
+	ActionMaximize
+	// ActionUnmaximize restores a maximized window.
+	ActionUnmaximize
+	// ActionFullscreen makes a window fullscreen.
+	ActionFullscreen
+	// ActionClose closes a window.
+	ActionClose
+	// ActionMove moves a window directed by the user.
+	ActionMove
+	// ActionResizeNorth resizes the top border of a window (directed by the user).
+	ActionResizeNorth
+	// ActionResizeSouth resizes the bottom border of a window (directed by the user).
+	ActionResizeSouth
+	// ActionResizeWest resizes the right border of a window (directed by the user).
+	ActionResizeWest
+	// ActionResizeEast resizes the left border of a window (directed by the user).
+	ActionResizeEast
+	// ActionResizeNorthWest resizes the top-left corner of a window (directed by the user).
+	ActionResizeNorthWest
+	// ActionResizeSouthWest resizes the bottom-left corner of a window (directed by the user).
+	ActionResizeSouthWest
+	// ActionResizeNorthEast resizes the top-right corner of a window (directed by the user).
+	ActionResizeNorthEast
+	// ActionResizeSouthEast resizes the bottom-right corner of a window (directed by the user).
+	ActionResizeSouthEast
+)
+
+// CursorName returns the cursor for the action.
+// It must be a single action otherwise the default
+// cursor is returned.
+func (a Action) CursorName() pointer.CursorName {
+	switch a {
+	case ActionResizeNorthWest:
+		return pointer.CursorTopLeftResize
+	case ActionResizeSouthEast:
+		return pointer.CursorBottomRightResize
+	case ActionResizeNorthEast:
+		return pointer.CursorTopRightResize
+	case ActionResizeSouthWest:
+		return pointer.CursorBottomLeftResize
+	case ActionResizeWest:
+		return pointer.CursorLeftResize
+	case ActionResizeEast:
+		return pointer.CursorRightResize
+	case ActionResizeNorth:
+		return pointer.CursorTopResize
+	case ActionResizeSouth:
+		return pointer.CursorBottomResize
+	}
+	return pointer.CursorDefault
+}
+
+func (a Action) String() string {
+	var buf strings.Builder
+	for b := Action(1); a != 0; b <<= 1 {
+		if a&b != 0 {
+			if buf.Len() > 0 {
+				buf.WriteByte('|')
+			}
+			buf.WriteString(b.string())
+			a &^= b
+		}
+	}
+	return buf.String()
+}
+
+func (a Action) string() string {
+	switch a {
+	case ActionMinimize:
+		return "ActionMinimize"
+	case ActionMaximize:
+		return "ActionMaximize"
+	case ActionUnmaximize:
+		return "ActionUnmaximize"
+	case ActionClose:
+		return "ActionClose"
+	case ActionMove:
+		return "ActionMove"
+	case ActionResizeNorth:
+		return "ActionResizeNorth"
+	case ActionResizeSouth:
+		return "ActionResizeSouth"
+	case ActionResizeWest:
+		return "ActionResizeWest"
+	case ActionResizeEast:
+		return "ActionResizeEast"
+	case ActionResizeNorthWest:
+		return "ActionResizeNorthWest"
+	case ActionResizeSouthWest:
+		return "ActionResizeSouthWest"
+	case ActionResizeNorthEast:
+		return "ActionResizeNorthEast"
+	case ActionResizeSouthEast:
+		return "ActionResizeSouthEast"
+	}
+	return ""
+}